Future developments for internal combustion engines are determined by various statutory requirements to reduce pollutant emissions and fuel consumption at the same time. One approach in this regard is the so-called homogeneous charge compression ignition (HCCI), which has been investigated extensively in recent times. In general, such homogeneous combustion processes implement concepts in which combustion of a homogeneous fuel/air mixture begins simultaneously throughout the entire combustion chamber. Such concepts exist for both gasoline engines (controlled auto ignition, CAI) and diesel engines (homogeneous charge late ignition, HCLI). However, it is characteristic of such methods as well as other low-emission combustion processes that the features of combustion are used as regulating variables, i.e., that a combustion regulation is carried out. The implementation of such methods thus necessitates the use of one or more combustion chamber sensors. The combustion chamber pressure sensor, i.e., cylinder pressure sensor, may be regarded as the state of the art here.
German Patent Application No. DE 10 2004 047 143 A1 describes a piezoelectric combustion chamber pressure sensor having a pressure-transmitting pin. A sensor element of a single-crystalline piezoelectric material is described therein for measuring the pressure in a combustion chamber of an internal combustion engine using a pressure-transmitting pin, a glow plug, which is displaceably mounted and protrudes into the combustion chamber, being provided as the pressure-transmitting pin. German Patent Application No. DE 10 2006 049 079 A1 describes a pressure measuring device for placement in a chamber of an internal combustion engine, having a housing, a force-transmitting element and a pressure sensor.
The cylinder pressure or the combustion chamber pressure in general is fundamentally a useful variable because it allows the calculation of a heating characteristic analysis, thus making characteristic variables of combustion, for example, the start of combustion, the location of combustion, or similar characteristic variables available for regulation. These variables are mostly used as a basis, in particular as regulating variables, of the aforementioned applications for gasoline and diesel engines. The manipulated variables of combustion regulation usually include exhaust gas recirculation rate (EGR), injection time and injection quantity. The exhaust gas recirculation rate is a characteristic variable in exhaust gas recirculation, which is used to reduce nitrogen oxides in gasoline engines, diesel engines or even in other internal combustion engines. Temperature peaks are lowered by exhaust gas recirculation. However, with the conventional manipulated variables, the exhaust gas recirculation rate plays a special role because changes in that rate do not have a direct effect on combustion due to the mixing in the intake area of the engine. During dynamic engine operation in particular, an effective exhaust gas recirculation rate cannot be given. However, cylinder pressure sensors are also of interest for conventional combustion processes in conjunction with cylinder-specific diagnostic functions. It would be desirable in general to have devices and methods which could be used in both gasoline engines and diesel engines and which permit operation of an internal combustion engine reliably and efficiently, in particular an internal combustion engine having direct injection and exhaust gas recirculation. The devices and methods should in particular provide an indicator for an efficient exhaust gas recirculation rate or an alternative indicator for an exhaust gas recirculation.